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Chris,
It may be possible to design a three phase saturable inductor (SR), but
a system of that complexity is above my pay grade.
I've never seen a three phase SR for sale, and I've had a standing
search for them on eBay for 7 or more years. They don't come up
frequently in any sort of incarnation. If such a beast exists,
instructions for designing one are probably proprietary to the engineers
at transformer builders.
You could certainly use three individual single phase reactors, one on
each leg, and drive them from a common control voltage source.
Come to think of it, if you are running three phase input power, that
would imply to me that you must be rectifying it and using a DC resonant
charged TC system. That would be an entirely different can of worms
than a straightforward AC driven TC system that I was referring to. I
don't know how a SR would work in a DC system, if at all. I'm not even
sure that throttling the primary side of your 3 phases input transformer
with a SR would produce the desired level of control after the AC is
rectified.
A SR doesn't reduce the voltage output of your power transformer like a
Variac does. It just limits the amount of power that can be drawn from
the system, by limiting the amount of current available to the primary
of the PT.
The DC resonant charging systems that I've seen use gapped inductors
between the rectifier output and the gap. Richie Burnett's site in
England has extensive info on DC resonant systems. See:
Perhaps you could wind a heavy coil on the center of an E-I core system,
and mechanically vary the gap opening with a machine screw. You might
even be able to use the original primary winding of a sacrificial
industrial power transformer of the appropriate rating, and ignore all
of the other windings. If you have access to an industrial water jet
cutter, then opening the core to gap it would be straightforward.
Otherwise, be prepared to spend a LONG afternoon with a hacksaw and a
bottle of liniment.
I suspect that the current setting would be sensitive to tiny changes in
the gap spacing, and you would have to have a pretty rigid setup from a
mechanical standpoint for reliable operation. All of the gapped inductor
systems that I've seen have insulating fish paper or sheet plastic to
maintain the gap at a fixed distance. There would be strong
electromagnetic forces that would try to pull the gap together as the
current in the inductor increases.
Dave
On 10/4/2015 11:58 AM, Chris Boden wrote:
This is very interesting stuff. The thing I notice is, does anyone make (or
have detailed instructions on building) a saturable reactor for 3-Phase
power? At 480VAC? I'm really interested in this as a solution. Given the
nature of what we do (and how impressive it is when it goes wrong.....which
happens a lot....) I would much rather use a heavy iron and copper system
than a nice tiny modern silicon system for this application.
Sometimes, low-tech is better. Especially when you make a living by using
products "in a manner inconsistent with its labeling" as our insurance
company likes to say. ;)
Thank you everyone for the replies!